This invention generally relates to computer aided detection and diagnosis (CAD) of radiographic images. More particularly, this invention relates to a method and system for computer aided detection and diagnosis of dual energy (“DE”) or multiple energy images.
The classic radiograph or “X-ray” image is obtained by situating the object to be imaged between an X-ray emitter and an X-ray detector made of photographic film. Emitted X-rays pass through the object to expose the film, and the degree of exposure at the various points on the film are largely determined by the density of the object along the path of the X-rays.
It is now common to utilize solid-state digital X-ray detectors (e.g., an array of switching elements and photo-sensitive elements such as photodiodes) in place of film detectors. The charges generated by the X-rays on the various points of the detector are read and processed to generate a digital image of the object in electronic form, rather than an analog image on photographic film. Digital imaging is advantageous because the image can later be electronically transmitted to other locations, subjected to diagnostic algorithms to determine properties of the imaged object, and so on.
Dual energy (DE) imaging in digital X-Ray combines information from two sequential exposures at different energy levels, one with a high energy spectrum and the other with a low energy spectrum. With a digital X-ray detector, these two images are acquired sequentially to get two additional images, a soft tissue image and a bone image. A multiple energy imaging system can be built that can be used to further decompose the bone and tissues in an anatomy. A series of images at different energies/kVps (Energy 1, . . . Energy n) can be acquired in a rapid sequence and decomposed into bone and different tissue types (Tissue 1, . . . . Tissue m).
Diagnosis from radiographic images has traditionally been a visual task. Due to the subjective nature of the task, the diagnosis is subject to inter- and intra-reader variability. In addition, due to the underlying and overlying structures relevant to the pathologies of interest, visual assessment can be difficult. Subtle rib fractures, calcifications, and metastatic bone lesions (metastases) in the chest can be difficult to detect on a standard chest X-ray. As an additional example, only 5-25% of pulmonary nodules are detected today with chest radiographs, but 35-50% are visible in retrospect.